A Power over Ethernet (POE) technology refers to that power is provided for an access device, such as an Internet Protocol (IP) telephone, a camera, or an access point (AP), using the Ethernet.
Generally, a POE system includes power sourcing equipment (PSE) and a powered device (PD). The PSE supplies power to the PD using the Ethernet, and also is a manager of a Power over Ethernet process in the entire POE system.
When the PSE supplies power to the PD over the Ethernet, a network cable power loss is caused, and the PSE needs to reserve network cable power loss, to meet a power requirement of the PD. Currently, the PSE performs power reservation according to a maximum network cable loss in a worst case (a loss caused when a network cable has maximum direct current impedance and a length of 100 meters) defined in a standard. However, in an actually deployed POE system, a network cable loss is not always a loss in the worst case. Therefore, a power that needs to be reserved for the network cable loss may be very small. If the PSE always performs power reservation according to the maximum network cable loss in the worst case, PSE power is wasted, and usage of the PSE power is reduced.